Similar hydraulic filters and filter apparatus are readily available on the market in a plurality of embodiments (e.g., DE 197 11 589 A1). In addition to suction filter apparatus, filter apparatus as return line filters, in-line filters, or ventilation filters are known. In generic terms they are often referred to as hydraulic filters. Generally, these hydraulic filters are devices for separation of solids, with fibrous, grainy, or lattice-shaped filter media being used to separate solids from liquids or for separating dusts from gases.
Furthermore, other separation devices in the prior art (e.g., DE 42 14 324 A1) are cyclones which are devices with which the action of a centrifugal force separates particles of solids from gases or liquids which are subsumed in the jargon under the generic term fluid. In the aforementioned solution, the cyclone is located in a ventilation path leading from a driving mechanism space (crank space) to the intake line of an internal combustion engine so that aerosols entrained by the air are separated in the cyclone and can be delivered by an outlet to an oil sump of the internal combustion engine. To be able to prevent unwanted feed of oil from the oil sump into the cyclone even under extreme operating conditions, a stop safeguard in the form of a float valve is on the outlet side.
This cyclone separation technology has also already been used in combination with filter devices. Thus, DE-OS 37 35 106 discloses a process for separating liquid particles from gases, in particular in the form of aerosols from exhaust gases, in which the gases are centrifuged first and then filtered. Some of the filtrate gases are then relayed to a cyclone. The liquid particles entrained in the gas flow are combined into droplets by frequent deflection of the direction of their motion (swirling flow). The droplets emerge by their own weight from of the separation device.
Furthermore, U.S. Pat. No. 6,129,775 A discloses a cyclone separator with a predominantly conically running separation housing in which, following the wall of the separation housing and with the formation of a swirl space spaced analogously, a usually self-contained guide body enables improved swirl guidance for separating the particles in the swirl space for a tangentially supplied fluid flow with particle fouling. Filtration by a filter element is not possible with the known solution.
The prior art (e.g., EP 06 59 462 A1) also discloses solutions in which, for further particle separation, in the bypass flow of a cyclone separator a filter element is held in a separate filter housing following in the direction of the fluid stream. The filtration line of these known solutions still leaves much to be desired.